1. Field of the Invention
The present invention generally relates to hydrocarbon detectors and, in particular, to those detectors used for determining the presence of liquid hydrocarbon substances.
2. Statement of the Prior Art
Instruments for detecting the presence of oil and related hydrocarbon substances have been in use for many years. One variety of such instruments which has lately become increasingly popular is one which includes those instruments used for distinguishing between water and hydrocarbon liquids. Such instruments are usually used to detect either the contamination of water by hydrocarbon substances or the contamination of hydrocarbon substances with water. The wide scale presence of hydrocarbon substances such as oil and gasoline in our environment and their wide spread use in society necessitates that such instruments be readily available and widely used in order to insure a healthy environment and to avoid long term, large scale pollution of our environment. For these reasons, such sensors have been extensively developed and are generally based on a wide variety of operating principles or characteristics of the liquids being detected. These operating principles generally include electrical conductivity, thermal conductivity, liquid density, light transmission, and even the solubility of various materials in hydrocarbon environments. Such systems are exemplified by a number of United Sates patents describing a wide variety of instruments. For example, U.S. Pat. Nos. 3,800,219 and 4,131,773 describe instruments which are based upon the operating principle that the electrical conductivity of water is greater than the electrical conductivity of oil and related hydrocarbon substances. While the '219 patent describes a complicated mechanism for taking a sample of liquid from the top surface of a body of water, the '773 patent describes a sensor having a pair of electrodes submerged in water and another pair of electrodes enclosed in an oleophatic material floating on the surface of the water. The characteristic that the thermal conductivity of water is greater than that of oil and related hydrocarbon substances is used as an operating principle in U.S. Pat. Nos. 4,221,125, 4,135,186, and 4,116,045. These instruments generally include the application of a constant predetermined amount of heat to a thermal sensor and one or more measurements of the temperature of that sensor before and/or after that application of heat. The physical property of liquid density is used as the operating principle in instruments described by U.S. Pat. Nos. 3,918,034 and 3,946,625. These patents both use the floatation level of a float to trip a magnetic reed switch to thereby signal the presence of the lighter density oil and related hydrocarbon substances. The principle of light transmission is used by an instrument described in Japanese Pat. No. 52-17891. Lastly, the solubility of various substances in oil and related hydrocarbon substances is used as the operating principle in a sensor described by U.S. Pat. No. 3,720,797. In this sensor, a spring loaded switch is encased and held open by a material which is soluble in gasoline and similar hydrocarbon liquids in water. The presence of such hydrocarbons causes the encasing material to dissolve and allows the switch to close and thus signal the presence of such substances. These devices, of course, are not the only ones which make use of their respective operating principles but have been chosen for description here as being exemplary of the various approaches taken. This wide variety of instruments and the development work which has gone into them is good evidence of the strong need for such instruments. Unfortunately, the instruments detailed above are rather complex in their manufacture and/or use. Wherever there is such a large need for any sort of a sensing element, such an element which includes the qualities of simplicity and inexpensiveness will always be welcomed.